1. Field of the Invention
The present invention relates to a moirxc3xa9 image capturing apparatus and a method therefor for measuring a three-dimensional object through a non-contact optical method by application of a moirxc3xa9 imaging technique.
2. Brief Description of the Prior Art
Generally, a variety of techniques have been widely used for measuring smooth curves of a three-dimensionally shaped object (hereinafter referred to as an object) in a number of fields such as inspection of various products, CAD/CAM, medical science, solid modeling and so on.
Such conventional techniques have been performed by utilization of a contact type of three-dimensional measuring apparatus, with which all the points of curved surfaces of an object have been detected for precise measurement. However, there is a disadvantage in the aforementioned conventional method in that each and every point of three-dimensional curved surfaces of an object should be detected to thereby consume a great deal of time in going over all measuring processes.
In order to solve the aforementioned problem, a so-called moirxc3xa9 imaging technique has been recently developed and used for measuring an object in a non-contact method. The moirxc3xa9 imaging method has an advantage in significantly reducing the time taken for all the measuring steps in comparison with the conventional contact type method for measuring an object.
On the other hand, such a moirxc3xa9 imaging technique includes a step of illuminating light to an object to form a predetermined pitch of striped patterns which makes it possible to obtain a moirxc3xa9 image having three-dimensional shape information on the object. Then, the moirxc3xa9 image goes through a precise actuating procedure.
In the non-contact type device for measuring an object to accomplish the aforementioned moirxc3xa9 imaging method, a glass grating with a pattern of stripes carved on one side surface of the glass and drawn in chrome at a predetermined pitch is projected to the object by an optical projection unit. Also, grating actuating means is needed for actuating the striped glass grating so that striped patterns projected to the object are shifted by a predetermined pitch.
In other words, if the striped glass grating shown in FIG. 1a is projected to the object, a pattern of straight lines is formed on the object as shown in FIG. 1b. Such a pattern of straight lines results in a pattern of curved lines correspondingly to the height of topographical lines to be drawn in accordance with a three-dimensional shape of the object.
On the other hand, if the object drawn with a pattern of curved lines shown in FIG. 1b is overlapped with the striped glass grating shown in FIG. 1a, there appears an image of a pattern of wavy lines, a so-called moirxc3xa9 image. Since such a moirxc3xa9 image is a pattern of topographical lines formed according to different heights of a surface of the object, it is possible to measure the three-dimensional shape of the object through interpretation of the resultant moirxc3xa9 image.
FIG. 2 is a schematic view for illustrating a phase shifting type of a moirxc3xa9 image capturing apparatus, one of the most widely used conventional moirxc3xa9 image capturing devices.
As shown in FIG. 2, the conventional moirxc3xa9 image capturing apparatus includes white light source, a condenser, a projection grating and a projection lens. In addition, a grating actuator is included in the conventional apparatus for actuating projection grating at a predetermined pitch through 3 to 5 steps.
Furthermore, the conventional moirxc3xa9 image capturing apparatus also includes an imaging lens for receiving the light reflected at the object, reference grating identically structured to the projection grating, relay lens and a charge coupled device (hereinafter referred to as CCD) camera array.
In the conventional moirxc3xa9 image capturing apparatus thus constructed, if light illuminated by the white light source is condensed through the condenser and projects the projection grating through the projection lens to the object, the projected grating results in a pattern of striped lines in accordance with the three-dimensional shape of the object as shown in FIG. 1b. 
The striped pattern of the object sequentially passes through the imaging lens and relay lens to form an image on the CCD camera. The image formed on the CCD camera, as shown in FIG. 1c, is made by combining an image of the reference grating (refer to FIG. 1a) and a moirxc3xa9 image of the striped pattern (refer to FIG. 1b).
However, in the conventional moirxc3xa9 image capturing device, the moirxc3xa9 image of striped pattern having information on the three-dimensional volume of the object is combined with the image of the reference grating and the resultant image is simultaneously formed on the CCD camera, so that an additional unit is needed for removing the image of reference grating, complicating the structure of the device.
In addition, in order to measure the three dimensional shape of an object with the conventional moirxc3xa9 image capturing apparatus, it is necessary to properly adjust all the measurement specifications to an object such as size, vertical step coverage, measurement precision and so on. A number of projection gratings drawn with various patterns of straight lines with different pitches should be equipped to fully satisfy all the measurement specifications, so as to increase manufacturing and purchasing cost.
There is another disadvantage in the conventional moirxc3xa9 image capturing apparatus in that it is necessary to spend a great deal of time on frequently changing and accurately arranging the glass gratings with different pitches of straight line patterns to meet such a variety of measurement conditions.
Furthermore, there is still another disadvantage in the conventional moirxc3xa9 image capturing apparatus in that it is necessary to include an additional grating actuator for actuating the straight line pattern formed on the glass grating to a desired position, thereby requiring increase in the volume and additional manufacturing cost of the apparatus.
Therefore, it is an object of the present invention to solve the aforementioned problems and provide a moirxc3xa9 image capturing apparatus constructed in a simpler structure by removing a reference grating, which also offsets a need for removing an image of the reference grating.
It is another object of the present invention to provide a method for capturing a moirxc3xa9 image without using a reference grating.
It is a third object of the present invention to provide a moirxc3xa9 image capturing apparatus which can swiftly and conveniently adjust a pitch of grating patterns and actuate a resultant moirxc3xa9 image with a rotatable polygon mirror controlled by operations of a software program.
It is a fourth object of the present invention to provide a method for capturing a moirxc3xa9 image by swiftly and conveniently adjusting a pitch of grating and actuating the moirxc3xa9 image with a rotatable polygon mirror controlled by operations of a software program.
In order to accomplish the aforementioned object of the present invention, there is provided a moirxc3xa9 image capturing apparatus in accordance with a preferred embodiment of the present invention, the apparatus comprising:
an optical projection unit arranged in perpendicular to a reference surface with a light source for illuminating light to the reference surface, where an object is positioned, and a projection grating installed on a optic axis between the light source and the reference surface for projecting the light generated by the light source toward the object; and
an optical imaging unit arranged in perpendicular to the reference surface with an imaging lens for making an image with the light reflected at the object and a light receiving part installed on the same optic axis as that of imaging lens for receiving the light passing through the imaging lens to turn into a moirxc3xa9 image.
In accordance with a first embodiment of the present invention, there is also provided a method for capturing a moirxc3xa9 image, the method comprising the steps of:
letting the light generated by a light source illuminate through a projection grating to an object positioned at a reference surface; and
receiving the light reflected at the object through an imaging lens to capture a moire image by a difference in phases of the reference surface and the object.
There is also provided a moirxc3xa9 image capturing apparatus in accordance with a second embodiment of the present invention, the apparatus comprising:
a light source for illuminating light;
polygonal reflecting surfaces rotating means for rotating a plurality of reflecting surfaces at which the light of the light source reflects;
lens means for transforming the spot beam generated by the light source into slit-beam to form a striped pattern;
light traveling route probing means for generating a synchronizing signal by probing a traveling route of the light after reflection at the reflecting surfaces of the polygonal reflecting surfaces rotating means; and
control means for controlling an on/off switching period of the light source and a pitch of the striped pattern according to the synchronizing signal of the light traveling route probing means.
There is provided a moire image capturing apparatus in accordance with a third embodiment of the present invention, the apparatus comprising:
a light source for illuminating light;
lens means directly connected with the light source for transforming spot beam of the light source into slit-beam;
polygonal reflecting surfaces rotating means for rotating a plurality of reflecting surfaces to reflect the light illuminated by the light source and lens means and thereby form a striped pattern;
light traveling route probing means for generating a synchronizing signal by probing a traveling route of the light after reflection at the reflecting surfaces of the polygonal reflecting surfaces rotating means; and
control means for controlling an on/off switching period of the light source and a pitch of the striped pattern according to the synchronizing signal of the light traveling route probing means.
In accordance with another embodiment of the present invention, there is also provided a method for capturing a moire image, the method comprising the steps of:
transforming spot beam generated by a light source into slit-beam;
allowing the slit-beam to reflect at least one of reflecting surfaces of polygonal reflecting surfaces rotating means that rotates at a high speed; and
allowing a pitch of the slit-beam having reflected at the polygonal reflecting surfaces rotating means to change by adjusting an on/off switching period of the light source.